Oh it already happened and man, I turned around to run (yeah, I ran away) and bumped to one of my friends, and asked me, why I'm red all over my face. Oh and I also saw his... erm... and I was so embarrassed to no end, and it got repeated, again, to another crush of mine, and I vowed to never looked at him again though it didn't come true cause day after tomorrow he went to our house with his little sister and I was all red again. Why do boys sometimes forget to close the door?

if he is in the shower and is standing tall and naked?
---i'll pause, stare at him from top to bottom then up again... give a direct eye contact and muttered an "oooopsss.... sorry.."
then turn my back and head out... then laugh about it.

well you'd have to be stalking the person in the first place to see them bathing. So if i was already in that creepy situation... id just keep watching... probably pull out a video, steal her clothes and see what happens